GEOPRIV M. Thomson
Internet-Draft Andrew Corporation
Intended status: Standards Track B. Rosen
Expires: September 29, 2011 Neustar
D. Stanley
Aruba Networks
G. Bajko
Nokia
A. Thomson
Cisco Systems, Inc.
March 28, 2011
Relative Location Representationdraft-ietf-geopriv-relative-location-01
Abstract
This document defines an extension to PIDF-LO (RFC4119) for the
expression of location information that is defined relative to a
reference point. The reference point may be expressed as a geodetic
or civic location, and the relative offset may be one of several
shapes. Optionally, a reference to a secondary document (such as a
map image) can be included, along with the relationship of the map
coordinate system to the reference/offset coordinate system to allow
display of the map with the reference point and the relative offset.
Also included in this document is a Type/Length/Value (TLV)
representation of the relative location for use in other protocols
that use TLVs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 29, 2011.
Copyright Notice
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Internet-Draft Relative Location March 2011
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Internet-Draft Relative Location March 20111. Introduction
This document describes a format for the expression of relative
location information.
A relative location is formed of a reference location, plus a
relative offset from that reference location. The reference location
can be represented in either civic or geodetic form. The reference
location can also have dynamic components such as velocity. The
relative offset is specified in meters using a Cartesian coordinate
system.
In addition to the relative location, an optional URI can be provided
to a document that contains a map, floorplan or illustration.
Applications could use this information to display the relative
location. Additional fields allow the map to be oriented and scaled
correctly.
Two formats are included: an XML form that is intended for use in
PIDF-LO [RFC4119] and a TLV format for use in other protocols such as
those that already convey binary representation of location
information defined in [RFC4776].
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Overview
This document describes an extension to PIDF-LO [RFC4119] as updated
by [RFC5139] and [RFC5491], to allow the expression of a location as
an offset relative to a reference.
This extension effectively allows the creator of a location object to
include two location values plus an offset. The "baseline" location
that is given outside of the <relative-location> element is what will
be visible to a client that does not understand that extension (i.e.,
one that ignores the <relative-location> element). A client that
does understand this extension will interpret the location within the
relative element as a refinement of the baseline location, which
gives the reference location for the relative offset.
Creators of location objects with relative location thus have a
choice of how much information to put into the "baseline" location
and how much to put into the "reference" location. For example, all
location information could be put inside the <relative-location>
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element, so that clients that do not understand relative location
would receive no location information at all. Alternatively, the
baseline location value could be precise enough to specify a building
that contains the relative location, and the reference location could
specify a point within the building from which the offset is
measured.
The baseline location SHOULD be general enough to describe both the
reference location and the relative location (reference plus offset).
In particular, while it is possible to put all location information
into the "reference" location (leaving an universally broad
"baseline"), location objects SHOULD NOT have all location
information in the baseline location. Doing this would cause clients
that do not understand relative location to incorrectly interpret the
baseline location (i.e., the reference point) as the actual, precise
location of the client.
Both the baseline and the reference location are defined either as a
geodetic location [OGC.GeoShape] or a civic address [RFC4776]. If
the baseline location was expressed as a geodetic location, the
reference MUST be geodetic. If the baseline location was expressed
as a civic address, the reference MUST be a civic.
Baseline and reference locations MAY also include dynamic location
information [RFC5962].
The relative location can be expressed using a point (2- or
3-dimensional), or a shape that includes uncertainty: circle, sphere,
ellipse, ellipsoid, polygon, prism or arc-band. Descriptions of
these shapes can be found in [RFC5491].
Optionally, a reference to a 'map' document can be provided. The
reference is a URI. The document could be an image or dataset that
represents a map, floorplan or other form. The type of document the
URI points to is described as a MIME media type. Metadata in the
relative location can include the location of the reference point in
the map as well as an orientation (angle from North) and scale to
align the document CRS with the WGS-84 CRS. The document is assumed
to be useable by the application receiving the PIDF with the relative
location to locate the reference point in the map. This document
does not describe any mechanisms for displaying or manipulating the
document other than providing the reference location, orientation and
scale.
As an example, consider a relative location expressed as a point,
relative to a civic location:
<presence xmlns="urn:ietf:params:xml:ns:pidf"
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Internet-Draft Relative Location March 20114. Relative Location
Relative location is a shape (point, circle, ellipse...). The shape
is defined with a CRS that has a datum defined as the reference
(which appears as a civic address or geodetic location in the tuple),
and the shape coordinates as meter offsets North/East of the datum
measured in meters (with an optional Z offset relative to datum
altitude). An optional angle allows the reference CRS be to rotated
with respect to North.
4.1. Relative Coordinate System
The relative coordinate reference system uses a coordinate system
with two or three axes.
The baseline and reference locations are used to define a relative
datum. The reference location defines the origin of the coordinate
system. The centroid of the reference location is used when the
reference location contains any uncertainty.
The axes in this coordinate system are originally oriented based on
the directions of East, North and Up from the reference location: the
first (x) axis increases to the East, the second (y) axis points
North, and the optional third (z) axis points Up. All axes of the
coordinate system use meters as a basic unit.
Any coordinates in the relative shapes use the described Cartesian
coordinate system. In the XML form, this uses a URN of
"urn:ietf:params:geopriv:relative:2d" for two-dimensional shapes and
"urn:ietf:params:geopriv:relative:3d" for three-dimensional shapes.
The binary form uses different shape type identifiers for 2D and 3D
shapes.
Dynamic location information [RFC5962] in the baseline or reference
location alters relative coordinate system. The resulting Cartesian
coordinate system axes are rotated so that the 'y' axis is oriented
along the direction described by the <orientation> element. The
coordinate system also moves as described by the <speed> and
<heading> elements.
4.2. Placement of XML Elements
The baseline of the reference location is represented as <location-
info> like a normal PIDF-LO. Relative location adds a new <relative-
location> element to <location-info> Within <relative-location>
<reference> and <offset> elements are described. Within <offset> are
shape elements described below.
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Internet-Draft Relative Location March 20114.3. Binary Format
This document describes a way to encode the relative location in a
binary TLV form for use in other protocols that use TLVs to represent
location.
A type-length-value encoding is used.
+------+------+------+------+------+------+------+
| Type |Length| Value ...
+------+------+------+------+------+------+
| X | N | Value label ...
+------+------+------+------+------+------+------+
Figure 1: TLV-tuple format
Type field (X) is defined as a single byte. The type codes used are
registered an IANA managed 'RLtypes' registry defined by this
document, and restricted to not include the values defined by the
CAtypes registry. This restriction permits a location reference and
offset to be coded with unique TLVs.
The Length field (N) is defined as an unsigned integer that is one
byte in length. This field can encode values from 0 to 255. The
length field describes the number of bytes in the Value. Length does
not count the bytes used for the Type or Length.
The Value field is defined separately for each type.
Each element of the relative location has a unique TLV assignment. A
relative location encoded in TLV would have the baseline location
TLVs, a reference location TLV which contains within it the reference
refinement TLVs. The reference TLVs are followed by the relative
offset, and optional map TLDs described in this document.
4.4. Distances and Angles
All distance measures used in shapes are expressed in meters.
All orientation angles used in shapes are expressed in degrees.
Orientation angles are measured from WGS84 Northing to Easting with
zero at Northing. Orientation angles in the relative coordinate
system start from the second coordinate axis (y or Northing) and
increase toward the first axis (x or Easting).
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Internet-Draft Relative Location March 20114.5. Value Encoding
The binary form uses single-precision floating point values [IEEE754]
to represent coordinates, distance and angle measures. Single
precision values are 32-bit values with a sign bit, 8 exponent bits
and 23 fractional bits.
Binary-encoded coordinate values are considered to be a single value
without uncertainty. When encoding a value that cannot be exactly
represented, the best approximation is chosen according to
[Clinger1990].
4.6. Relative Location Restrictions
More than one relative shape MUST NOT be included in either a PIDF-LO
or TLV encoding of location for a given reference point.
Any error in the reference point transfers to the location described
by the relative location. Any errors arising from an implementation
not supporting or understanding elements of the reference point
directly increases the error (or uncertainty) in the resulting
location.
4.7. Baseline TLVs
Baseline TLVs are defined in [RFC3825].
4.8. Reference TLV
When a reference is encoded in binary form, the baseline and
reference locations are combined in a reference TLV. This TLV
contains civic address TLVs (if the baseline was a civic) or geo TLVs
(if the baseline was a geo).
+------+------+------+------+------+------+
| 111 |Length| Reference TLVs |
+------+------+------+------+------+------+
Reference TLV
If this TLV contains the reference location, then we need to
explicitly say that the shape TLVs in here use WGS84; and when the
shapes are outside of this, they use the relative:2d or relative:3d
forms.
TBD - Need TLVs for dynamic objects (orientation - multiple angles,
speed - single scalar, heading - multiple angles)
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Internet-Draft Relative Location March 20114.9. Shapes
Shape data is used to represent regions of uncertainty for the
reference and relative locations. Shape data in the reference
location uses a WGS84 [WGS84] CRS. Shape data in the relative
location uses a relative CRS.
The XML form for shapes uses Geography Markup Language (GML)
[OGC.GML-3.1.1], consistent with the rules in target="RFC5491"/>.
Reference locations use the CRS URNs specified in [RFC5491]; relative
locations use either a 2D CRS (urn:ietf:params:geopriv:relative:2d),
or a 3D (urn:ietf:params:geopriv:relative:3d), depending on the shape
type.
The binary form of each shape uses a different shape types for 2d and
3d shapes.
Nine shape type codes are defined.
4.9.1. Point
A point "shape" describes a single point with unknown uncertainty.
It consists of a single set of coordinates.
In a two-dimensional CRS, the coordinate includes two values; in a
three-dimensional CRS, the coordinate includes three values.
4.9.1.1. XML encoding
A point is represented in GML using the following template:
<gml:Point xmlns:gml="http://www.opengis.net/gml"
srsName="$CRS-URN$">
<gml:pos>$Coordinate-1 $Coordinate-2$ $Coordinate-3$</gml:pos>
</gml:Point>
GML Point Template
Where "$CRS-URN$" is replaced by a
urn:ietf:params:geopriv:relative:2d or
urn:ietf:params:geopriv:relative:3d and "$Coordinate-3$" is omitted
if the CRS is two-dimensional.
4.9.1.2. TLV encoding
The point shape is introduced by a TLV of 113 for a 2D point and 114
for a 3D point.
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+------+------+
| 113/4|Length|
+------+------+------+------+
| Coordinate-1 |
+------+------+------+------+
| Coordinate-2 |
+------+------+------+------+
| (3D-only) Coordinate-3 |
+------+------+------+------+
Point Encoding
4.9.2. Circle or Sphere Shape
A circle or sphere describes a single point with a single uncertainty
value in meters.
In a two-dimensional CRS, the coordinate includes two values and the
resulting shape forms a circle. In a three-dimensional CRS, the
coordinate includes three values and the resulting shape forms a
sphere.
4.9.2.1. XML encoding
A circle is represented in and converted from GML using the following
template:
<gs:Circle xmlns:gml="http://www.opengis.net/gml"
xmlns:gs="http://www.opengis.net/pidflo/1.0"
srsName="urn:ietf:params:geopriv:relative:2d">
<gml:pos>$Coordinate-1 $Coordinate-2$</gml:pos>
<gs:radius uom="urn:ogc:def:uom:EPSG::9001">
$Radius$
</gs:radius>
</gs:Circle>
GML Circle Template
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A sphere is represented in and converted from GML using the following
template:
<gs:Sphere xmlns:gml="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/pidflo/1.0"
srsName="urn:ietf:params:geopriv:relative:3d">
<gml:pos>$Coordinate-1 $Coordinate-2$ $Coordinate-3$</gml:pos>
<gs:radius uom="urn:ogc:def:uom:EPSG::9001">
$Radius$
</gs:radius>
</gs:Sphere>
GML Sphere Template
4.9.2.2. TLV encoding
A circular shape is introduced by a type code of 115. A spherical
shape is introduced by a type code of 116.
+------+------+
| 115/6|Length|
+------+------+------+------+
| Coordinate-1 |
+------+------+------+------+
| Coordinate-2 |
+------+------+------+------+
| (3D-only) Coordinate-3 |
+------+------+------+------+
| Radius |
+------+------+------+------+
Circle or Sphere Encoding
4.9.3. Ellipse or Ellipsoid Shape
A ellipse or ellipsoid describes a point with an elliptical or
ellipsoidal uncertainty region.
In a two-dimensional CRS, the coordinate includes two values, plus a
semi-major axis, a semi-minor axis, a semi-major axis orientation
(clockwise from North). In a three-dimensional CRS, the coordinate
includes three values and in addition to the two-dimensional values,
an altitude uncertainty (semi-vertical) is added.
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An ellipse is introduced by a type code of 117 and an ellipsoid is
introduced by a type code of 118.
+------+------+
| 117/8|Length|
+------+------+------+------+
| Coordinate-1 |
+------+------+------+------+
| Coordinate-2 |
+------+------+------+------+
| (3D-only) Coordinate-3 |
+------+------+------+------+------+------+------+------+
| Semi-Major Axis | Semi-Minor Axis |
+------+------+------+------+------+------+------+------+
| Orientation | (3D) Semi-Vertical Axis |
+------+------+------+------+------+------+------+------+
Ellipse or Ellipsoid Encoding
4.9.4. Polygon or Prism Shape
A polygon or prism include a number of points that describe the outer
boundary of an uncertainty region. A prism also includes an altitude
for each point and prism height.
At least 3 points MUST be included in a polygon. In order to
interoperate with existing systems, an encoding SHOULD include 15 or
fewer points, unless the recipient is known to support larger
numbers.
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Internet-Draft Relative Location March 20114.9.4.1. XML Encoding
A polygon is represented in and converted from GML using the
following template:
<gml:Polygon xmlns:gml="http://www.opengis.net/gml"
srsName="urn:ietf:params:geopriv:relative:2d">
<gml:exterior>
<gml:LinearRing>
<gml:posList>
$Coordinate1-1$ $Coordinate1-2$
$Coordinate2-1$ $Coordinate2-2$
$Coordinate3-1$ ...
...
$CoordinateN-1$ $CoordinateN-2$
$Coordinate1-1$ $Coordinate1-2$
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
GML Polygon Template
Alternatively, a series of "pos" elements can be used in place of the
single "posList". Each "pos" element contains two or three
coordinate values.
Note that the first point is repeated at the end of the sequence of
coordinates and no explicit count of the number of points is
provided.
A GML polygon that includes altitude cannot be represented completely
in binary. When converting to the binary representation, a two
dimensional CRS is used and altitude is removed from each coordinate.
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+------+------+
|119-21|Length|
+------+------+------+------+------+------+
| Count | (3D-only) Height |
+------+------+------+------+------+------+
| Coordinate1-1 |
+------+------+------+------+
| Coordinate1-2 |
+------+------+------+------+
| (3D-only) Coordinate1-3 |
+------+------+------+------+
| Coordinate2-1 |
+------+------+------+------+
...
+------+------+------+------+
| CoordinateN-1 |
+------+------+------+------+
| CoordinateN-2 |
+------+------+------+------+
| (3D-only) CoordinateN-3 |
+------+------+------+------+
Polygon or Prism Encoding
Note that unlike the polygon representation in GML, the first and
last points are not the same point to be the same in the TLV
representation. The duplicated point is removed from the binary
form.
4.9.5. Arc-Band Shape
A arc-band describes a region constrained by a range of angles and
distances from a predetermined point. This shape can only be
provided for a two-dimensional CRS.
Distance and angular measures are defined in meters and degrees
respectively. Both are encoded as single precision floating point
values.
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locates the reference or offset within the map. Maps can be simple
images, vector files, 2-D or 3-D geospatial databases, or any other
form of representation understood by both the sender and recipient.
4.10.1. Map URL
In XML, the map is a <map> element defined within <relative-location>
and contains the URL. The URL is encoded as a UTF-8 encoded string.
An "http:" or "https:" URL MUST be used unless the entity creating
the PIDF-LO is able to ensure that authorized recipients of this data
are able to use other URI schemes. A "type" attribute MUST be
present and specifies the kind of map the URL points to. Map types
are specified as mime media types as recorded in the IANA Media Types
registry. For example <map type="image/png">https://www.example.com/
floorplans/123South/floor-2</map>. In binary, the map type is a
separate TLV from the map URL:
+------+------+------+------+------+-- --+------+
| 123 |Length| Map Media Type ...
+------+------+------+------+------+-- --+------+
| 124 |Length| Map Image URL ...
+------+------+------+------+------+-- --+------+
Map URL TLVs
4.10.2. Map Coordinate Reference System
The CRS used by the map depends on the type of map. For example, a
map described by a 3-D geometric model of the building may contain a
complete CRS description in it. For some kinds of maps, typically
described as images, the CRS used within the map must define the
following:
o The CRS origin
o The CRS axes used and their orientation
o The unit of measure used
This document provides elements that allow for a mapping between the
local coordinate reference system used for the relative location and
the coordinate reference system used for the map where they are not
the same.
4.10.2.1. Map Reference Point Offset
This optional element identifies the coordinates of the reference
point as it appears in the map. This value is measured in a map-type
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dependent manner, using the coordinate system of the map.
For image maps, coordinates start from the upper left corner and
coordinates are first counted by column with positive values to the
right; then rows are counted with positive values toward the bottom
of the image. For such an image, the first item is columns, the
second rows and any third value applies to any third dimension used
in the image coordinate space.
The <offset> element contains 2 (or 3) coordinates similar to a GML
"pos", For example:
<offset> 2670.0 1124.0 1022.0</offset>
Map Reference Point Example XML
+------+------+
| 125 |Length|
+------+------+------+------+
| Coordinate-1 |
+------+------+------+------+
| Coordinate-2 |
+------+------+------+------+
| (3D-only) Coordinate-3 |
+------+------+------+------+
Map Reference Point Coordinates TLV
If omitted, a value containing all zeros is assumed. If the
coordinates provided contain fewer values than are needed, the first
value from the set is applied in place of any missing values.
4.10.2.2. Map Orientation
The map orientation includes the orientation of the map direction in
relation to the Earth. Map orientation is expressed relative to the
orientation of the relative coordinate system. This means that map
orientation with respect to WGS84 North is the sum of th orientation
field, plus any orientation included in a dynamic portion of the
reference location. Both values default to zero if no value is
specified.
This type uses a single precision floating point value of degrees
relative to North.
In XML, the <orientation> element contains a single floating point
value, example <orientation>67.00</orientation>. In TLV form:
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+------+------+------+------+------+------+
| 126 |Length| Angle |
+------+------+------+------+------+------+
Map Orientation TLV
4.10.2.3. Map Scale
The optional map scale describes the relationship between the units
of measure used in the map, relative to the meters unit used in the
relative coordinate system.
This type uses a sequence of IEEE 754 [IEEE.754] single precision
floating point values to represent scale as a sequence of numeric
values. The units of these values is dependent on the type of map,
and could for example be pixels per meter for an image.
A scaling factor is provided for each axis in the coordinate system.
For a two-dimensional coordinate system, two values are included to
allow for different scaling along the x and y axes independently.
For a three-dimensional coordinate system, three values are specified
for the x, y and z axes.
Alternatively, a single scaling value MAY be used to apply the same
scaling factor to all coordinate components.
Images that use a rows/columns coordinate system often use a left-
handed coordinate system. A negative value for the y/rows-axis
scaling value can be used to account for any change in direction
between the y-axis used in the relative coordinate system and the
rows axis of the image coordinate system.
In XML, the <scale> element may contain the single scale value, or
may contain 2 (or 3) values similar to a GML "pos" with separate
scale values. In TLV form:
+------+------+------+------+------+
| 127 |Length| Scales ...
+------+------+------+------+------+
Map Scale TLV
4.10.3. Map Example
An example of expressing a map is:
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<xs:simpleType name="doubleList">
<xs:list itemType="xs:double"/>
</xs:simpleType>
</xs:schema>
xml schema relative-location
7. Security Considerations
This document describes a data format. To a large extent, security
properties of this depend on how this data is used.
Privacy for location data is typically important. Adding relative
location may increase the precision of the location, but does not
otherwise alter its privacy considerations, which are discussed in
[RFC4119]
[[Not that interesting, but it could be relevant ?]] The fractional
bits in IEEE 754 [IEEE.754] floating point values can be used as a
covert channel. For values of either zero or infinity, non-zero
fraction bits could be used to convey information. If the presence
of covert channels is not desired then the fractional bits MUST be
set to zero. There is no need to represent NaN (not a number) in
this encoding.
8. IANA Considerations8.1. Relative Location Registry
This document creates a new registry called 'Relative Location
Parameters'. As defined in [RFC5226], this registry operates under
"IETF Consensus" rules.
The content of this registry includes:
Relative Location Code: Numeric identifier, assigned by IANA.
Brief description: Short description identifying the meaning of the
element.
Reference to published specification: A stable reference to an RFC
which describes the value in sufficient detail so that
interoperability between independent implementations is possible.
IANA is requested to not permit values to be assigned into this
registry which conflict with values assigned in the CAtypes registry
or to permit values to be assigned into the CAtypes registry which
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